Federal and state requirements have mandated substantial reductions in carbon particulate matter (PM, so called soot), hydrocarbons, nitrogen oxides and carbon monoxide emission for gasoline and diesel engines. Attempts at reducing such emissions, in particular attempts to reduce particulate emissions from diesel engines, include catalytic diesel particulate filters (DPF) in which a catalytically active material is dispersed within a substrate in the particulate filter. The catalyst promotes removal (e.g., oxidation) of particulates and other pollutants of diesel fuel combustion in the exhaust gas stream.
Applying a catalytic material (also referred to herein as a washcoat) to the DPF substrate is one of the most promising technologies for effective removal (combustion) of trapped PM. In general, better catalytic performance is achieved by increasing washcoat loading so as to increase the concentration of catalytically active material present. However, an increase in washcoat loading can result in an increase in flow restriction when exhaust gas flows by the catalytic particulate filter. This increase of exhaust gas flow restriction results in an increase in exhaust line backpressure, which could be detrimental to engine performance and fuel economy. In general, the lower the backpressure, the better the engine performance and fuel economy will be. Accordingly, a need exists for a particulate filter that provides for reduction of particulates in the exhaust gas while minimizing backpressure caused by the particulate filter.